Compressor



Nov. 1, 1938 B. V. E. NORDBERG 2,134,834

COMPRESSOR Original Filed Nov. 13, 1935 6 Sheets-sheet 1 Ermentor 155mm VE HQ ZAJ g wdn Gttornegs COMPRESSOR Original Filed Nov. 13, 1935 6 Sheets-Sheet .2

'55 Lhe.

555mm 31. mm

I 1 I ll ZSnnentor (Itforue Nov. 1, 1938. B. V. E. NORDBERG 2,134,834

COMPRESSOR Original Filed Nov. 15, 1935 6 Sheets$heet 4 3nnentor 55mm EFT 1W (Ittomegs 193s. B.v. E. NORDBERG 2,134,834

COMPRESSOR Original Filed Nov.'l3, I935 6 Sheets-Sheet 6 Enventor aim/nay L ln zbbemy attorneys stares rarest orrrce aliases colaranssoa ltruno V. Nordberg, lldilwaultee, Willa, assignor to Nordlrerg Manufacturing @ompany, ll llilwau lree, Wis, a corporation of Wisconsin Application November lltl, 1935, Serial No. tlltm l ltenewed Olctober 29, 1937 2h @llaiins. (til. 23il=-2dl This invention relates to compressors and pan variable duration establish a variable loade 'tlcularly to unloading means therefor. condition in response to demand.

In compressors with mechanically operated lhe controller contains not only means for valves it has been proposed to unload the comgenerating the necessary pressure impulses but 5 pressor variably by varying the timing of the also servo-motor means for controlling the do, inlet valves and similar schemes have been proration of such impulses, in response to receiver posed for compressors having suction operated pressure or other demand indicator. In this (sometimes called automatic) inlet valves. way a self-contained and highly responsive as applied to the latter class of compressors, mechanism is p vi Such units m y b unloading may be effected in either of two ways manufactured to control any desired number to (l) holding the inlet valves closed commencing of working spaces malting up a single stage or at a variable point in the suction stroke and multi-stage compressor. Such units may be continuing until the piston reaches the same timed simply by setting the actuating cams on point in the compression stroke, and (2) holdthe cam shaft.

ing the inlet valve open for a variable period ihe invention will now he described as on ill during the initial portion of the compression plied to a two stage, two cylinder double-acting stroke. Broadly stated, the two schemes are C p e so having Cranks ell t Ell-611 equivalent in that they vary the weight of gas compressor has four working spaces and the iiicompressed per cycle (a cycle comprising a suclet valves for the four spaces operate at so" tlonand ensuing compression stroke) but the intervals. Consequently the unloaders tor the second method is usually preferred, because cylfour working spaces operate at similar intervals.

inder pressure approximates suction pressure In the drawings,- during the unloaded portion of the cycle and Fig. l is a plan view of a compressor of. the the tendency toward leakage and thermal losses type stated, with the invention applied. consequently is less. Fig. 2 is a head-end elevation thereof. The present invention is applicable to com- Fig. 3 is a fragmentary section transverse to pressors having suction operated inlet valves, the axis of a cylinder through the center line and is applicable to either type of unloading of one of the two low pressure head end inlet operation just mentioned. Obviously the timvalves with its unloading motor.

ing of the valve controllers relatively to the cycle Fig. 4 is a section through the center line of so would be different in the two cases, and the the same inlet valve, the plane of section being controllers in one case would hold the inlet valves taken in the direction of the axis of the cylinder. closed and in the other would hold the valves F g- 5 s a SectiOnal P Vi f a Controller open, but the basic principle of the mechanism for controlling e iifleli Valves 0if u WOYkiIlg herein described and claimed would be the same Spac sv The Plane of Section is indicated all; 35

in the two cases. 5-5 on Fig 6.

As stated, the second scheme of operation is a Fig. 6 is a section on the line 6-6 of Fig. ii preferred, and to. simplify the disclosure, the (i. e. through the impul e generator 01 the low invention will be described as embodied in a p u e ead end inlet valve unloader).

system of this type. Fig. l is a section on the line 'l-'l of Fig. 5. so

The invention proposes a control unit driven Referring first to Figs. 1 and 2, the foundation in timed relation to the compressor crank shaft, or bed of the Compressor is indicated at ii, theand acting through liquid pressure lines to dc- 10W pressmie fram? at the h1g1} pressure a liver suitably timed impulses to unloader moframe at H and the ,crank 3 tors which control the automatic inlet valves. crank shaft M turns bearmgs t frames A Single means responsive to receiver pressure and I3 and as usual reciprocates pistons one in the low pressure cylinder l5 and another in the equwalent dmand mdlcator) plogressi'veiy high pressure cylinder H5. The drive from crank vanes the f og of Flpulses relative-y shaft to pistons is conventional; and is effected to the strokes in w 1ch un oadmg occurs. Thus through the usual cranks (here set at to 5 the unloading action may be effective progreseach other) connecting rods, crossheads and sively in y degree from full load no load piston rods, one of each for each piston. These Ac o d to the Preferred arrangement parts are not visible in the. drawings because inlet valve unloader motors are normally biased they are enclosed. A portion of the low presto no load position and the impulses by their sure piston appears at ii in Fig. 4.

drawings the pipes 35 are c The compressor may be o ab.=.e means, but a s1 ihrcnous wheel type is convent nally indie to The intake or suction. is leads to pa valves having bonnets 22 on the lo at both ends of the low pressure The low pressure cylinder discharges pairs of automatic discharge valves "nai nets 22 on the upper side and at both the low pressure cylinder !5, and thence tercooler 23 to the inlet valves having 24 on the upper side and at both ends high pressure cylinder E5. The high cylinder discharges through. the automati charge valves having bonnets 25 on the low 2 and. thence through pipe 28 to the in which the compressed gas do through pipe 28 to any point of The inlet valves will be described as o reed or feather type, described and ciai in the patent to Nordberg 1,570,392, J2. 1926, are structurally siniflar for inde: The discharge valves may he, and erably are of the same type, thugh any sui discharge valve, automatic or or. Discharge valves are necessary,

. .able portion of the discharge kill the corresponding working space) a permit he valve to close. T"..ese motors described in detail hereinai'te oiled by a corresponding imp a, timer contained in housing I: i. 32 0' this mechanism is o. i 4 at the same angular velocit, chain 33. Receiver pressure pipe 34 the timer mechanism in housing 3 timer mechanism serving to vary the d the generated impulses in response to tions of receiver pressure. There is an impulse generator for each group of similarly timed inlet legends l. h. e. for the low 1 c. e. for he low pressure crank arly h. h. e. and h. c. e. for t 1e ugh pressure cylinder.

Referring now to Figs. 3 and i winch s 'iow' of the head end inlet valves in place in 1 pressure cylinder, it will be observed that cylinder (5 has a head 36 with cooling jac space 31, and that the cylinder barrel is cored to produce the usual jacket, portions of which ap pear at 38, and an inlet passage 39 leading to inlet valves from the inlet connection 59 loca'ecl at mid-length of the cylinder (see Fig. 1). In Fig. 4 the piston I! is shown at the head end dead point. Note that the rings 4i approach but do not overtravel the inlet port 42.

Seated in rib 43 surrounding port 42 and sealed thereto by gasket 44 is the grid-like valve seat member 45. The seat member 45 is held in place by studs 46 threaded in bonnet 2i and engaging in thrust the inverted V-shaped wires 41. One end of each stud is swiveled in the corresponding yoke 41, as indicated at 49. The yokes 4'! are cast as a unit with ring 48 and are connected to the seat member 45 by machine screws 5|. The construction is such that if the nuts 52 which hold the bonnet 2| in place on the cylinder be i. ob

i and. conrle re s r W va.

his

ort slots 5: 5 each con". e1 and associated. bloiwsprir' L is es ialiy the construction of the Ivorclberg patent a' ove identified.

unseat the re valve e'ements 5c ".ie ii loading opera there is provided 2. yo "'ying two corrili e nents E32, Whose teetl".

t through 2 in the seat ed valves it; .e yoke is carried. 5 i plunger ii in a hub :ed on. the rectangular vol or whose upper a combined spri g seat es, as clee 'lurg'e" Oi ovement of he upper e tee. by collision of t *lfhe impulse pig" valve iilustra'tec. communicates '5 cans or into the bonnet and pen passage fo 4 space in. cylinoer c urges the plunger t. fluid. a the inner end of the piston "E22 may eves lng Ti and. move the plunger M i.

The spring 1 directioi'i, that in a direction to fret comb teeth 53 out of engagement with the v. 58.

Briefly stated, in the absence of preset ing on the plunger H the spring ii moves combs in to hold the inlet valves unseatecl. admission of pressure fluid against the pin retracts the combs and permits the inlet to perfor 1 th r normal functions.

Broadly considered, this typical of any automatic inlet valve wit -eans operative QJ'LCIHZL tively to hold the in. t valve comtantly open or to permit it to close function normally. The arrangement is peculiar in the fact that the mechanism is biased by the spring "ii in an unloading dlrection and loading is produced by the admission of pressure fluid to the actuating oiston.

The mechanism which develops against the plunger 12 timed fluid pressure impulses will now be described with reference to Figs. 5, 6 and is set at 180 from the cam 83 1. h. e.

7. The pressure fluid is conveniently, but not necessarily oil. In the following description oil is disclosed as the pressure transmitting fluid, but without any limiting implication. The housing 3| described in connection with Figs. 1 and 2 is an oil sump or reservoir through which the shaft 32 extends, the shaft being mounted in bearings 8| and being sealed against oil leakage at 82. The shaft 32 carries four actuating cams which correspond to the inlet valves for the four working spaces of the compressor. These cams are angularly spaced according. to the timing of the inlet valves of the four working spaces of the compressor, that is to say, the cam 83 l. c. e. Similarly the cam 83 h. h. e. is at 180" from the cam 83 h. c. e. The first two cams which operate respectively the crank end and head end unloaders for the low pressure cylinders, are displaced 90 from the second set of cams which operate, respectively, the head end and crank end unloaders for the high pressure cylinders. Each of these cams operates an impulse mechanism and since these are identical a description of a single one will suffice. Fig. 6 shows the impulse mechanism for the low pressure head end inlet valves.

While the earns 83 have been differentiated as to the particular inlet valve which they control it is deemed unnecessary to apply the distinguishing letters to the apparatus actuated by the cams, it being understood that these various mechanisms are duplicates.

The cams 83 each operate a corresponding oil displacing plunger 84. Each is reciprocated in the cylinder by the cam and each is urged toward the cam by a coil compression spring 85. 86 is a valve which is normally closed and which is provided to insure filling of the plunger space with oil, since the presence of compressible gas in the cylinder would affect the timing. The space below the plunger 84' communicates with a corresponding impulse pipe 35, the particular impulse pipe illustrated in Fig. 6 being that connected to the low pressure head end inlet valve, as indicated by the legend 35 l. h. e. Communication from the space below the plunger 84 to the pipe 35 is afforded by the passage 81. Interposed between the passage 81 and the sump within the casing 3| is a combined admission and spill-back valve 88. This is a simple poppet valve seating against flow from the passage to the sump, urged in a closing direction by a coil spring 88, and capable of being unseated by thrust exerted through stem 9| which is in telescopic thrust relation with the pilot of the valve 88. The stem 9| is held in alinement with the valve by its telescopic engagement and is guided to reciprocate longitudinally through the guide bearing 92. It is normally retracted to permit the valve 88 to seat by means of a coil compression spring 93 which reacts between the guide plate 92 and a spring seat 94 which is adjustable onthe stem 9| by means of a nut 95. A shaft 98 is rotatable in bearings 90 within the housing 3|, the shaft 96 being parallel with the shaft 32 The shaft 96 carries a number of alined eccentrics 81, one corresponding to each of the plungers' 84, and journaled on each eccentric 91 is a rock lever 98, one end of which is in thrust engagement with the upper face of a lug 99 on the corresponding plunger 84, and the other end of which is in thrust engagement with the adjust- .able tappet |8I on the corresponding stem 8|. the example shown,'the tappet IN is threaded on the push rod 9| and vertical adjustment relatively to the push rod is afforded in this manner.

As the plunger 84 is depressed its related rock lever 98 turns in a counterclockwise direction, permitting a related upward movement of the corresponding valve 88. Rotation of the shaft 98 in reverse directions raises or lowers eccentric 91 and thus varies the point in the downward stroke of the plunger 84 at which the spill back valve 88 will seat. When the valve 88 does seat the oil displaced by the plunger 84 will flow through the corresponding pipe 35, in this case 35 l. h. e. and cause retraction of the unloading plunger of the corresponding inlet valve. Each plunger 84 displaces more than sufiicient oil to move a corresponding plunger I2 through its full stroke, and it is therefore necessary to provide for each passage 81 a relief valve I82. This relief valve takes the form 01' a poppet valve opening away from the passage 81 and discharging into a manifold I83 which forms part of a pressure accumulator hereinafter described.

I The valve I 82 is urged to its seat by a light coil compression spring I84. The seat for the valve I82 is formed in the bushing I85 which is mounted in a cavity in the base of the housing 3| and held-in place by a plug I86 threaded into the base and engaging the bushing I85 through pressure equalizing thrust ball I 81 and an associated cap member I88.

The excess oil discharged to the passage I83 which receives excess oil from all the plungers 84, leads to an accumulator cylinder I89 (see Figs. 5 and 7). This accumulator cylinder is provided with a plunger I II which is spring loaded by a coil compression spring II2. Pressure in the accumulator assists in holding valves I82 seated, so in effect this is a loaded relief valve. The load on the spring H2 is adjusted by shifting the spring seat H3. Adjustment is effected by turning the threaded rod H4, which is swiveled at H5 in the seat 3 and which is threaded in the closure. H8. A look nut II'I is provided to preserve the adjustment. To prevent the development of fluid pressure above plunger III, a vent H9 is provided.

Oil entering the chamber I89 forces the piston III upward against the resistance of spring H2 and excess oil discharges to the oil sump through a relief port H8. The effect is to establish and maintain, during the operation of the device, a supply of oil under pressure in the accumulator I89, and this oil is supplied from the excess delivered by the various impulse generators. The valves I82 prevent back flow to the passages 81 and maintain the isolation of the passages 81 s from one another. a

Formed in the base of the housing 3| is a cylinder which receives a differential piston I2I. This offers at its lower end I22 a piston head of large effective area and affords by means of a shoulder or offset I23 an annular piston head of smaller effective area. The piston is guided, and the upper end of the working space for the annular piston head I23, is closed by a guide sleeve I24 fixedly mounted on the base of the housing 3|.

The piston I2| has an axial bore in which is mounted a balanced piston valve having an upper head I25 and a lower head I26 separated by an intervening groove. The valve is balanced by means of a port I21 extending from the space above the upper head I25 tothe space below the lower head I26. A passage I28 leads from the accumulator space I88 to the working space above the annular piston head I23, and a passage I29 leads from this space through the piston to the space around the reduced middle portion of the piston valve. The space above the upper head communicates with the oil sump in housing 3I by way of passage I3I. The upper valve head I25 has very slight lap at its upper and lower edges over a port I32 connected by passage I33 with the space below the large piston head I22 of the piston I2I. A bushing I30 threaded into a bore in the piston I2I serves as a limit stop for the piston valve.

It is obvious that if the two opposed working spaces of the piston I2I are connected together the piston will move upward because the larger effective area will predominate. On the other hand, if they are disconnected, and if the larger space be then vented back to the sump, the piston vn'llmove downward. The head I25 with its very slight lap on port I32 establishes these connections selectively, and it will be obvious from a consideration of Fig. '7 that the piston I2I will follow the valve head I25 in its upward and downward movements.

The piston I2I is provided near its upper end, with rack teeth I34 which coact with a sector gear I35 on shaft 96, which is the shaft on which the control eccentrics 91 are mounted, The position of the valve head I25 is adjusted by means responsive to the demand for compressed air, and in the example illustrated this means. is a device responsive to pressure in the high pressure receiver 21. Many different arrangements might be used, but as a simple example, there has been chosen a differential bellows mechanism.

Mounted in housings I36 and I31 are metal bellows I38 and a slightly smaller metal bellows I39. The interior of both bellows are subject to pressure in the receiver 21 communicated by way of the pipe 34 (Figs. 1, 2 and '7) and the passages I4I and I42. The bellows act in opposi tion to each other through a longitudinally shiftable rod I 43. The purpose of using two bellows of differential areas is to secure a relatively small effective area with parts of substantial size. While the bellows themselves offer some elastic resistance to displacement it is sometimes desirable to modify this and permit adjustment of the yielding resistance by using a light compression spring I44 whose stress is adjustable by shifting the collar I45 on the rod I43. This spring is shown confined between the end of housing I31 and the collar I45 and the collar may be clamped in adjusted position by means of a set screw I46.

Pivoted on a fixed fulcrum at I41 is a bell crank lever I48, one of whose arms is connected to the rod I43 by a link I49 and the other of whose arms is connected to the stem of valve I25 by means of link II. It will be observed that on rising receiver pressure, and defining direction with reference to Fig. 7, the rod I43 will move to the right, swinging the bell crank I48 clockwise and lowering the valve I25. Since the piston I2I follows the valve the piston will move downward turning the shaft 96 counterclockwise and lowering the eccentrics 91. The lowering of the eccentrics 91 causes the valves 88 to close later in the displacement stroke of their related plungers 84.

Since the delivery of pressure to the pressure motors on the inlet valves terminates the unloading action, delay in the closure of the valves 88 increases the unloading action. The shaft 32 is so timed relatively to the crank shaft I4 that each of the cams 83 sarts to depress its plunger 84 at such time that each corresponding plunger I2 is raised just prior to the commencement of the discharge stroke in the corresponding working space of the compressor. The range of adjustment afforded by rotation of the *shaft 96 is such that in the uppermost position of the eccentrics 91 the valve 88 will be allowed to close with the plunger 84 in its uppermost position. Similarly the eccentrics 91 are in their lowermost position and the valves 88 are not allowed to close throughout the entire downward stroke of the plunger 34. It is apparent, therefore, that the adjustment of the shaft 96 provides progressive adjustment from full capacity to a completely unloaded condition, and the adjustment of the shaft 91 is responsive to variation of receiver pressure through narrow limits determined by the operation of the bellows mechanism.

There is an important consideration affecting the design of the cams 83. The comb blades 63 should be so timed in their operation that they engage the inlet valve 58 when the valve is open and prevent the valve from closing, but they should never engage the valve 58 when the latter is closed. The function of the combs is to prevent the valves from moving from an open to a closed position. It is never their function to move the valves from a closed to an open position. Obviously, if the blades 63 come into action only when the valves are open the force which they exert will be minimized and injury to relatively delicate valves will be avoided.

The desired result can be secured by designing the cams 83 in such a way that they produce downward motion of corresponding plungers 84 through more than 180 of rotation of shaft 32. A satisfactory value is 225 of rotation. The unloading action is effected during the discharge stroke. Under fullcapacity conditions the inlet valves are allowed to remain closed throughout the entire discharge stroke. Under completely unloaded conditions they are held open throughout the entire discharge stroke, and under partial capacity conditions they are held open from the beginning of the discharge stroke to a variable point in the stroke.

Thus the blades assume obstructing position before the end of the suction stroke when the inlet valves are open, and under full load condition are retracted not later than the dead point. The mechanism controlling their retraction should be so flexible as to allow them to remain retracted throughout the discharge stroke or to retract them at any point in the discharge stroke depending on the desired capacity. Having once been retracted they should not again be moved into position to hold the inlet valves open until the inlet valves have been opened by suction. Be-' cause of unavoidable clearance in some compressors the inlet valves may not open by suction until the suction stroke has proceeded through a substantial crank angle. To meet this condition plunger 84 may be made active from a point before' the end of one suction stroke to a point after the beginning of the next suction stroke.

A bypass valve I52, (Fig. 7) which normally is closed, may be opened by turning handle I53, and when open dissipates pressure in the accumulator I09, and passages 81 (since valves I02 will open under predominant pressure in passages 87). As a consequence the compressor will be unloaded.

The invention has a number of important advantages. The unloading means, that is the unloading plungers on the inlet valves, are biased in an unloading direction, making it relatively simiii (it'll amaea plc to start the compressor'under no load. The use of a liquid link to time the unloading mechanism minimizes lag such as would be occasioned by the use of a compressible medium, and thus insures precise timing. Experience with the device has shown that there is a slight time lag between the start of the downward motion of a plunger M and the response of the corresponding plunger it. This lag appears to be constant for any given installation and was readily compensated for by slightly advancing the cam shaft fit with respect to the crank shaft M of the compressor.

lit has heretofore been proposed to operate unloading motors by means of gas compressed by the compressor. This scheme is workable where air is being compressed, but is open to obvious objeotions when noxious gases are being compressed, because special means must be provided to prevent the slightest leakage.

The unloading means can be applied to existing compressors merely by equipping the inlet valves with the necessary unloading motors and by arranging the impulse and timing unit so that it is driven at the proper rate from the crank shaft of the compressor. The device can be arranged to unload any desired number 'of Working spaces and the earns 83 may be angularly displaced on the cam shaft to conform to any angular spacing of the compressor cranks.

The invention permits progressive unloading from full capacity to a fully unloaded condition different mechanisms by the exercise of ordinary mechanical skill.

What is claimed is,--

l. The combination of a compressor of the expansible chamber type adapted to perform successive operating cycles; an unloading device having two positions, in one of which it renders the compressor inoperative and in the other of which it renders it operative; means biasing said unloader toward one of said positions; a pressure motor serving when energized to shift said unloader to the other of said positions; an impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pres sure transmitting connection between said impulse piston and said pressure motor; and adjustable means for venting said connection throughout a variable portion of thedisplacing stroke of said impulse piston.

2. The combination of a compressor of the expansible chamber type adapted to perform successive operating cycles; an unloading device having two. positions, in one of which it renders the compressor inoperative and in the other of which it renders itoperative; means biasing said unloader toward one of said positions; a pressure motor serving when energized to shift said un loader to the other of said positions; an impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pres sure transmitting connection between said impulse piston and said pressure motor; adjustable means for venting said connection throughout a variable portion of the displacing stroke of said impulse piston; and means responsive to the pressure established by the operation oi the compressor for adjusting the last-named means.

3. The combination of a compressor oi the expansible chamber type adapted. to perform successive operating cycles; an unloading device having two positions, in one of which it renders the compressor inoperative and in the other of which it renders it operative; means biasing said unloader toward the first named of said positions; a pressure motor serving when energized to shift said unloader to the second-named of said positions; an'impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pressure transmitting connectionbetween said impulse piston and said pressure motor; and adjustable means for venting said connection throughout a variable portion or the displacing stroke of said impulse piston.

i. The combination of a compressor oi the expansible chamber type adapted to perform successive operating cycles; an unloading device having two positions, in one of which it renders the compressor inoperative and in the other of which it renders it operative; means biasing said unloader toward one of said positions; a pressure motor serving when energized to shift said unloader to the other of said positions; an impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pressure transmitting connection between said impulse piston and said pressure motor; normally closed venting means for said connection; adjustable means for opening said venting means through a variable portion of the displacing stroke of said impulse piston; and means for adjusting the last-named means.

5. The combination of a compressor having a cylinder, a coacting piston, and an inlet valve; unloading means having two positions, in one of which itrenders the inlet valve inoperative and ilti in the other of which it permits the inlet valve tooperate; means biasing said unloading means to one of said positions; a pressure motor adapt ed when under pressure to shift said unloading means to the other of said positions; an impulse piston actuated in timed relation to the compressor piston; means establishing a fluid pres sure transmitting connection between the im pulse piston and the pressure motor; adjustable meansfor venting said connection through a variable portion of the displacing stroke of said impulse piston; and means for adjusting the last-named means.

6. The combination of a compressor having a cylinder, a coacting piston, and an inlet valve; unloading means controlling said inlet valve and biased to a position in which it holds the inlet valve open; a fluid pressure operated unloader motor associated with said unloading means and adapted when under pressure to shift said unloading means to a position in which it permits the inlet valve to close; an impulse piston actuated in timed relation to the compressor piston; means for establishing a fluidv pressure transmitting connection between the impulse piston and the unloader motor; adjustable means for venting said connection through a variable portion of the displacing stroke of said impulse piston; and means for adjusting the last-named means.

'7. The combination of a compressor of the expansible chamber type adapted to perform SUCCGSS unloadcr draulic pix. to shii't sair; tions: i in "irned re; tlon and navy displaceu. :nt means for transmittir or the impulse piste. nection through variab The combinati 2. expansible chamber typ cessive operating cycles; having two positions, in one o the compressor inoperative and in the other e. which it renders it operative; means blasts" said unloader toward one of said positions draulic pressure motor serving when energized to shift said unloader to the other of said po sitions; a hydraulic impulse piston actuated in timed relation to the cycles of the compressor and having a displacement which exceeds displacement of said hydraulic pressure moto means for establishing a hydraulic pressure transmitting connection between the impulse pie-- ton and said. hydraulic pressure motor, a loaded relief valve for permitting flow of excess hydraulic liquid from said connection; adjustable means for freely venting said connection through a variable portion of the displacing st pile of sa; impulse piston; and means responsive to a pres-- sure established by operation. or the compressor :for adjusting the last-named means.

5. line combination of a compressor having cylinder, coacting piston. and an inlet valve; an unloader having two positions, in one of which. it re ders said inlet valve inoperative and in the of ich it permits it to operate; means biascrig said unioader to one of said positions; hydraulic pressure motor adapted when subjected to 'f-IGSSUIB to shift said unloader to the other of said positions; a hydraulic impulse piston actu ate C. med relation to the compressor piston and ha? lg a, displacement which exceeds the displacement of he hydraulic motor; means for establishing a hydraulic pressure transmitting con nection between the impulse piston and the hydrauli motor; a loaded relief valve permitting flow of excess hydraulic liquid from said connection; and adjustable means operating in timed relation with the impulse piston for freely venting said connection through a variable portionof the displacing stroke of said impulse piston.

10. The combination of a compressor having a cylinder, a coacting piston and an inlet valve; shiftable means adapted to obstruct the closing movement of the inlet valve; means biasing said shifting means toward obstructing position; a hydraulic unloader motor serving when subjected to pressure to withdraw said obstructing means; a m'draulic impulse piston actuated in timed relation to the compressor piston and having a displacement which exceeds the displacement of the unloader motor; means for establishing a hydraulic pressure transmitting connection be- 11 ."olte of said. operated by pressure connected to adjust e." id acstable motion; means for shifting valve.

12. The combination of a compr having r a coacting piston and an inlet valve; 5 .or unloading said compressor by control- 1e action of the inlet valve; an unloadei piston for controlling said unloading n cans; an

1: to. no lie for establishing a hy sure t1. ansmittiiig connection betweei piston and the unloader piston; a znulator; 1C adecl relief valve for pelt.

tc-ass 11 raulic liquid under on. to said accuniulato be timed relation with the eely venting sa' connection 45 ,ble portion of the displac ng l npulse piston; a servos-not on assure from said acc'lnnldator,

and

r shifting the last-named valve.

The combination of a compressor havin a oer coacting piston and an inlet valve; :"table means having an inactive position, and 1. active position in which it serves to hold the inlet valve open; means biasing the lastmamed means to its active position; an unloader piston for forcing the means which holds the inlet valve open to its inactive position; an impulse piston ac tuated in timed relation to the compressor piston and having a displacement which exceeds the displacement of the unloader piston; means i 1' es tablishing a hydraulic pressure transmitting connection between the impulse piston and the unioader piston; a pressure accumulator; a loaded relief valve l or permitting flow of excess hydraulic liquid under pressure from said connection to said accumulator; adjustable means operated in timed relation with the impulse piston for freely venting said connection through a variable portion of the displacing stroke of said impulse piston; a servomotor operated by pressure from said accumulator, connected to adj st said adjustable means and including a valve which controls its motion; and means for shifting the last-named valve.

i l. The combination of a compressor having a cylinder and a coasting piston; unloading means for said compressor; an unloader piston for actuating said unloading means; an impulse piston actuated in timed relation to the compressor piston and having a displacement which exceeds the displacement of the unloader piston; means for iii lid

establishing a hydraulic pressure transmitting connection between. the impulse piston and the unloader piston; a pressure accumulator; a loaded relief valve for permitting flow of excess hydraulic liquid, under pressure from. said connection to said accumulator; adjustable means operated in timed relation with the impulse piston for freely venting said connection through a variable portion of the displacing stroke of said impulse piston; a servo-motor of the differential piston type including a balanced distributing valve, said servo-motor being operated by pressure fluid derived from said accumulator and being connected to: actuate said adjustable means; and. means for shifting said balanced distributing valve in response to variations of pressure developed. by the operation of the compressor.

he combination of a compressor having cyl' and a coacting piston; unloading means for the compressor; an unloader piston arranged to actuate said unloading means; an impulse piston actuated in timed relation to the "d esser piston and having a displacement exceeds the displacement oi the unloader piston; means for establishing a hydraulic pressure transmitting connection between the impulse piston and the unloader piston; a loaded relief valve ermitting flow of excess hydraulic liquid from said connection; a combined inlet and spill-back valve for permitting flow of liq-- uid to and from said connection; an adjustable actuating connection between the impulse piston and the last-named valve for holding the valve open during a variable portion of the displacing str'olre of the impulse piston; and means for adjusting said connection.

16. The combination of a compressor having a cylinder and a coacting piston; unloading means for the compressor; an unloader piston arranged toactuate said unloading means; an impulse piston actuated in timed relation to the compressor piston having a displacement which exceeds the displacement of the unloader piston; means for establishing a hydraulic pressure transmitting connection between the piston and the unloader piston; a loaded relief valve permitting flow of excess hydraulic liquid from said connection; a pressure accumulator fed thereby; a combined inlet and spill-back valve for permitting flow of hydraulic liquid to and from said connection; an adjustable actuating connection between the impulse piston and the last-named valve for holding the valye open during a variable portion of the displacing stroke of the impulse piston; means for adjusting said actuating connection; a servo-motor fed by said accumulator and connected to actuate said adjusting means, said servo-motor including a impulse said impulses, and serving to unload the compressor to a degree which varies with the duration of such impulses.

18. The combination of a compressor having successive operating cycles; liquid displacing means for developing liquid pressure impulses in timed relation to the operating cycles of the compressor; adjustable venting means adjustable while the compressor is running for varying the duration of such impulses; and unloading means controlled by said impulses, and serving to unload the compressor to a degree which varies with the duration of such impulses.

19. The combination of a compressor having a working space in which recurrent compression cycles are performed; an inlet valve of the suction operated type for such working space; pressure shiftable means for alternately permitting and suspending the normal operation of such inlet valve; at least one displacing means operated in timed relation with the compression cycles of the compressor to develop pressure impulses in said pressure shiitable means; adjustable venting means for varying the duration of such impulses; and means operable while the compressor is running for adjusting the last-named means.

20. The combination of a compressor having a working space in which recurrent'compression cycles are performed; an inlet valve of the suction operated type for such working space; pressure shiftable means for alternately permitting and suspending the normal operation of such inlet valve; displacing means operated in timed relation with the compression cycles of the compressor to develop pressure impulses in said pressure shiitable means; adjustable venting means for varying the duration of such impulses; an accumulator arranged to receive ere cess pressure fluid delivered by said displacing means; a servo-motor fed by said accumulator and connected to adjust said venting means, said servo-motor including a pilot valve which controlsits action; and means responsive to variations of pressure developed by operation of the compressor for shifting said pilot valve.

expansible chamber type adapted to perform successive operating cycles; an unloading device having two positions, in one of which it renders the compressor inoperative and in the other of which it renders it operative; means biasing said unloader toward one of said positions; a pressure motor serving when energized to shift said unloader to the other of said positions; an impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pressure transmitting connection between said impulse piston and said pressure motor; ad- \justable means for venting said connection throughout a variable portion of the displacing stroke of said impulse piston; and means operable to vent said connection continuously.

22. The combination of a compressor of the expansible chamber type adapted to perform successive operating cycles; an unloading device having two positions, in one of which it renders the compressor inoperative and in the other of which it renders it operative; means biasing said unloader toward one of said positions; a pressure motor serving when energized to shift said unloader to the other of said positions; an impulse piston actuated in timed relation to the cycles of the compressor; means establishing a fluid pressure transmitting connection between said impulse pi on and said I73 able means for venting said connection throi; out a variable portion of the displacing s of said impulse piston; means responsive to pressure established by the operation of compressor for adjusting the last named. means; and. means operable to vent said connection com tinuously.

23, The combi: ition of a compress a cylinder, a coacting piston and as shiftable means adapted. to obstruct the closing; movement of the inlet valve; means biasing saici shifting means toward obstructing position; unloader piston operable to withdraw said Oh" structing means; an impulse piston actuated in timed relation to the compressor plStOl 1d hav ing displacement which exceeds t.

ment the unloader piston; r for lisl'lin a hydraulic pressure tra tine excess hydraulic liquid lustable means operat in timed eely vent-- to vent said ding the st-named 1 which hold position; r cl :1 ti or the unloads; hydraulic pres tween. the impulse piss ton; a pressure accumulate for permi ting the flow of once under pressure from said conne cuinulato relation \vit one impulse piston fl ing said connection through a we of the displacing stroke of said inipuls a servoonotcr operated by pressure from s accumulator, connected to adjust said. adjusts, means and including a valve which controls ts motion; means for shifting the last-named valve; and means operable to vent said accumulator continuously.

25. The combination of a compressor having successive operating cycles; liquid. displacing means for developing liquid pressure impulses pressor in accorcla 'ce with such timing.

26. combin ion of a compressor having a Wor space in which recurrent compression cycles are performed; an inlet 'v'zlve of the suction operated type for such Wort 11;; space; pressure shiftable means for alternately permitting and suspending the normal operation of such inlet valve; at least one displacing means open eted in relation with. the compressi n cycles of the compressor to d veloo pressure im- W c'n phases is icl'l who is cf pulses in two phases, one 0 've, and the oi oi to actuate 531d press effective to vary tl cycle of the coir chance of phase occurs; While the compressor the lost'ne d means.

27. The combination of a compressor successive operating 03 clos each con v suction. stroke and a placement strol displacing r developing successive olraulic pressure in ulses Ollc iOl' each o i the comprcsso BRUllO 

